There is a parallel computer capable of communicating with an external network. FIG. 1 illustrates an example of a parallel computer that transmits and receives data to and from an external network. A parallel computer 1A in FIG. 1 includes a plurality of calculation nodes 11a, 11b, . . . that perform calculation processing and one I/O (Input/Output) node 12 connected to an NIC (Network Interface Card) 13 for communication with an external apparatus. Each of the calculation nodes and the I/O node includes a CPU (Central Processing Unit) and a router. Each calculation node 11 and the I/O node 12 are connected via the routers. The CPU of the I/O node 12 is connected to the NIC 13 and is capable of communicating with an external network 2A via the NIC 13.
As topologies for connecting a plurality of calculation nodes and an I/O node included in a parallel computer, a mesh, a torus, and the like are known. If a plurality of routes that can be selected are present between a transmission source calculation node and a destination I/O node, it is possible for each calculation node of the parallel computer to, even in a case where a failure occurs in a calculation node on a communication route, transmit data, making a detour to avoid the calculation node where the failure has occurred.
The following are related arts to the invention.                [Patent document 1]Japanese Patent Laid-Open Publication No. JP H10-69471        [Patent document 2]Japanese Patent Laid-Open Publication No. JP 2007-110240        